The invention is based on an unlockable non-return valve which is intended to be usable for very high system pressures and which has the features from the preamble of claim 1.
Non-return valves readily permit pressure medium to flow from a first orifice to a second orifice, with the closing element being raised from a seat counter to the force exerted by the pressure prevailing in the second orifice and counter to the force of the closing spring by means of a force produced by the pressure in the first orifice. Since the closing element is conventionally acted upon by the pressures on surfaces of identical size, a pressure arises in the first orifice which is higher than the pressure in the second orifice by a pressure difference which is equivalent to the force of the closing spring. The closing spring is only weak so as to keep the losses via the valve small, unless the intention is to deliberately build up the pressure medium in the first orifice. The flow through a non-return valve in the direction from the second orifice to the first orifice is possible only by additional measures through which an unlockable non-return valve is created. A poppet part is then provided which can act on the closing element in the opening direction and can raise it from the seat counter to the force of the closing spring and counter to the pressure difference between the first and second orifice.
DE 197 14 505 A1 has disclosed an unlockable non-return valve which has all of the features from the preamble of claim 1. The internal high-pressure forming of tubular semi-finished products is mentioned in the above-mentioned document as an example of use of a non-return valve of this type. The non-return valve which is shown has a valve housing having a continuous receiving bore which is stepped and is composed essentially of three sections. The diameter of the receiving bore is larger in the two outer sections than in a central section into which the two outer sections merge in steps lying in radial planes. High-strength inserts which are exposed to the system pressure and inserts serving to guide a poppet piston are placed into the two outer sections. The central section of the receiving bore is divided by a piston collar of the poppet piston into two annular spaces of which the one can be acted upon by control pressure via a pilot valve in order to control the non-return valve or can be relieved from pressure to a tank, and the other is permanently connected to a pressure-medium reservoir and contains a restoring spring for the poppet piston. It has been found that, in the known non-return valve, the poppet piston is not always smooth-running to the desired extent.
DE 198 56 018 A1 has also disclosed an unlockable non-return valve which has, all of the features from the preamble of claim 1 and which is likewise used, in particular, in plants for the internal high-pressure forming of tubular semi-finished products. In the non-return valve shown in DE 198 56 018 A1, the tendency of the poppet piston to jam has been reduced by the fact that the receiving bore has essentially the same diameter in the region of the inserts and between them, apart from short turned grooves in the axial direction which may be present, so that they can be machined from just one side of the valve housing, i.e. without changing the position of the valve housing or of the tool. A spacer bushing is arranged axially between two inserts, said bushing ensuring a fixed distance between two inserts on different sides of the piston, even when the diameter of the receiving bore remains constant. The insert which is close to the piston collar on each side of the piston collar is manufactured from a metallic material having good sliding properties, for example from a copper beryllium alloy, and has, at its inside diameter, a quite narrow clearance over its entire axial extent from the corresponding end section of the poppet piston, i.e. guides the corresponding end section tightly over its entire axial length. In spite of an obtained improvement over the non-return valve disclosed in DE 197 14 505 A1, even in the non-return valve according to DE 198 56 018 A1, jamming of the poppet piston has still been established at very high pressures.
The invention is therefore based on the object of developing an unlockable non-return valve having the features from the preamble of claim 1 in such a manner that the tendency of the poppet piston to jam is reduced.
According to the invention, this object is achieved in an unlockable non-return valve according to the preamble of claim 1 by the fact that this valve is additionally provided with the features from the characterizing part of claim 1. The invention is first of all based on the finding that the stiffness or even the jamming of the poppet piston in the known valves is also caused by deformation of the first inserts close to the piston collar. The deformation is caused by the high-pressure seal which is held in the turnout of the second insert and is supported axially on the first insert close to its inside diameter. At very high pressures, the force exerted on the first insert by the high-pressure seal is so large that the insert becomes deformed, its inside diameter, and the poppet piston becomes jammed.
According to the invention, first of all the first insert has a guide diameter for the end section of the poppet piston over just a short section of its end side facing the piston collar. Within the section described, the inside diameter of the insert is not reduced if the insert becomes deformed. Outside the section described, the inside diameter of the first insert is selected to be such a size that, in spite of a reduction in the inside diameter caused by the deformation, jamming of the poppet piston is still not caused. The supporting ring, which is situated axially between the high-pressure seal and the first insert in a receiving element which is formed between the two inserts and is open radially toward the end section of the poppet piston, has, at its outside diameter, a larger clearance in the receiving element, so that changes, which are caused by deformation, in the diameter of the receiving element do not have an effect on the supporting ring. The latter also has a substantially smaller outside diameter than the inserts, so that the engagement point of the force exerted by the high-pressure seal and the bearing point of the supporting ring against the first insert are situated axially at least approximately one above the other and the supporting ring is also hardly deformed directly. In spite of the narrow clearance between the supporting ring and end section of the poppet piston, the clearance preventing the high-pressure seal from migrating into the gap between the supporting ring and the end section of the poppet piston, in an unlockable non-return valve according to the invention, the force exerted by the high-pressure seal in the axial direction on the supporting ring and the first insert no longer causes the poppet piston to jam.
Advantageous refinements of an unlockable non-return valve according to the invention can be gathered from the subclaims.
As described in claim 2, the first insert preferably has, in front of its section with the guide diameter, a clearance of at {fraction (1/10)} mm, preferably of {fraction (2/10)} mm, radially with respect to the end section of the poppet piston. As a result, the distance from the poppet piston is sufficiently large in order, despite deformation, to avoid jamming. On the other hand, a radial seal between the insert and end section is still supported axially to such an extent that it does not migrate [lacuna] the gap which is present.
According to patent claim 3, the outside diameter of the supporting ring is approximately 1.1 times as large as the diameter of the turn-out for the high-pressure seal, i.e. extends radially only a relatively small distance beyond the high-pressure seal, so that a not all too large offset between the point at which the force is introduced by the high-pressure seal and the point at which the supporting ring bears against the first insert can occur.
According to patent claim 4, the radial clearance between the supporting ring and the end section of the poppet piston is very small, so that migration of a part of the high-pressure seal into the radial gap between the supporting ring and end section of the poppet piston is very reliably avoided.
Other advantageous developments of an unlockable non-return valve according to the invention are the subject matter of further subclaims.